mongo.rb in mongoid-3.0.1

- old
+ new

@@ -194,10 +194,11 @@
       #
       # @return [ Document ] The first document.
       #
       # @since 3.0.0
       def first
+        apply_id_sorting
         with_eager_loading(query.first)
       end
       alias :one :first
 
       # Create the new Mongo context. This delegates operations to the
@@ -401,20 +402,35 @@
         if spec = criteria.options[:hint]
           query.hint(spec)
         end
       end
 
+      # Apply an ascending id sort for use with #first queries, only if no
+      # other sorting is provided.
+      #
+      # @api private
+      #
+      # @example Apply the id sorting params.
+      #   context.apply_dd_sorting
+      #
+      # @since 3.0.0
+      def apply_id_sorting
+        unless criteria.options.has_key?(:sort)
+          query.sort(_id: 1)
+        end
+      end
+
       # Map the inverse sort symbols to the correct MongoDB values.
       #
       # @example Apply the inverse sorting params.
       #   context.apply_inverse_sorting
       #
       # @since 3.0.0
       def apply_inverse_sorting
         if spec = criteria.options[:sort]
           query.sort(Hash[spec.map{|k, v| [k, -1*v]}])
         else
-          query.sort({_id: -1})
+          query.sort(_id: -1)
         end
       end
 
       # Is the cache able to be added to?
       #